B-line scores and their correlation with the ratio of arterial partial pressure of oxygen to fractional inspired oxygen (PaO ₂ /FiO ₂ ) and fluid balance in post-operative cardiac surgery patients

Objective: Fluids are administered to optimize hemodynamics during off-pump coronary artery bypass grafting (CABG), which may lead to a positive fluid balance and increased lung water, lung congestion, hypoxemia, prolonged mechanical ventilation, and longer hospital stays. Lung ultrasound can assess extravascular lung water and help titrate diuretics and fluids, thus preventing hypoxemia. The primary objective of this study was to study the correlation between B-line scores measured by lung ultrasound and the PaO2 /FiO2 ratio (the ratio of arterial partial pressure of oxygen to fractional inspired oxygen) after off-pump CABG. Methods: Forty off-pump CABG patients were included in this prospective observational study in a tertiary care center from 2022 to 2023. The correlation coefficient from an earlier study was used and a sample size of 9 was calculated. Random sampling technique was used. A four-sector lung ultrasound was utilized for B-line scoring. B-line scores and PaO2 /FiO2 ratios were recorded at three time points: before the surgery commenced and at 24 and 48 hours post-operation. The fluid balance was calculated at 24 and 48 hours post-operation. Pearson correlation coefficient was used to evaluate the correlation between B-line scores and fluid balance with oxygenation, and its significance was assessed through a linear regression test. Results: The PaO2 /FiO2 ratio and B-line scores exhibited a statistically significant moderate negative correlation at 24 hours post-surgery (r=-0.44; SD=-0.66, 95% CI=-0.66, -0.15; P=0.004) and a B-line score exceeding 8 was associated with the lowest PaO2 /FiO2 ratio. However, fluid balance and PaO2 / FiO2 ratios revealed no correlation at 24 or 48 hours post-surgery. Additionally, fluid balance and B-line scores demonstrated a moderate positive correlation after 48 hours but no correlation at 24 hours post-surgery. Conclusion: B-line scores always negatively correlated with PaO2 /FiO2 ratios, and scores greater than eight corresponded to the lowest ratio.